System and method to extend low line operation of flyback converters

ABSTRACT

An amplifier system may include at least one input source, a flyback converter including a pair of complementary metal oxide silicon field effect transistor (MOSFETs), a controller integrated circuit (IC) having a quasi-resonant (QR) pin and configured to provide a biased drive current to the flyback converter, and a transition component arranged at the controller IC and configured to correct pulse width modulation at the IC to ensure the voltage at a transition pin of the IC is above a predefined threshold during a resonant transition.

TECHNICAL FIELD

Disclosed herein are systems and methods to extend low line operation offlyback converters.

BACKGROUND

Audio amplifiers and other applications often employ flyback convertersas a means to provide a bias supply to various circuits and integratedcircuits (ICs) on the primary and secondary sides. These bias powersupplies typically use off-the-shelf flyback controller ICs. To improveefficiency, quasi resonant and active clamp topology flyback convertersare used as the bias supply. These controller ICs may require that thevoltage on their quasi-resonant pin be high prior to a complementarymetal oxide silicon field effect transistor (MOSFET) turning on.However, at low line when the system is off, the voltage at the ICsresonant pin may take a longer period of time to transition to a highlevel and can result in the main MOSFET switch turning on again afterthe IC's internal time out. This phenomenon can result in hardswitching, ringing on the MOSFET's switch node, and even hard failure.Failure can lead to complete system shutdown due to lack of bias power.

SUMMARY

An amplifier system may include at least one input source, a flybackconverter including a pair of complementary metal oxide silicon fieldeffect transistor (MOSFETs), a controller integrated circuit (IC) havinga quasi-resonant (QR) pin and configured to provide a biased drivecurrent to the flyback converter, and a transition component arranged atthe controller IC and configured to correct pulse width modulation atthe IC to ensure the voltage at a transition pin of the IC is above apredefined threshold during a resonant transition.

An audio amplifier system employing flyback converters to provide a biassupply may include at least one input source, a flyback converterincluding a pair of complementary metal oxide silicon field effecttransistor (MOSFETs), a controller integrated circuit (IC) having aquasi-resonant (QR) pin and configured to provide a biased drive currentto the flyback converter, and a transition component arranged at thecontroller IC and configured to correct pulse width modulation at the ICto ensure the voltage at a transition pin of the IC is above apredefined threshold during a resonant transition.

An amplifier system may include at least one input source, a flybackconverter including a pair of complementary field effect transistors(FETs), a controller integrated circuit (IC) having a quasi-resonant(QR) pin and configured to provide a biased drive current to the flybackconverter, and a transition component arranged at the controller IC andconfigured to correct pulse width modulation at the IC to ensure thevoltage at a transition pin of the IC is above a predefined thresholdduring a resonant transition, wherein the transition component is a DCoffset arranged in series with the QR pin of the controller IC to offsetthe voltage above the predefined threshold.

BRIEF DESCRIPTION OF THE DRAWINGS

The system may be better understood with reference to the followingdrawings and description. The components in the figures are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention. Moreover, in the figures,like-referenced numerals designate corresponding parts throughout thedifferent views.

FIG. 1 illustrates an example circuit diagram for a flyback converterhaving a primary side and a secondary side;

FIG. 2 illustrates the primary side of the system of FIG. 1 ;

FIG. 3A illustrates example waveforms for the system of FIGS. 1 and 2when the AC Line voltage is low (e.g., 50 Vrms);

FIG. 3B is a zoomed view of a portion of FIG. 3A;

FIG. 4 illustrates an example circuit diagram for a flyback converter(primary side) with DC offset and fast dv/dt transition circuit added tothe controller's QR pin;

FIG. 5 illustrates an example system diagram for a flyback converter(primary side) with a resistor added between the controller's QR andoutput pins that facilitates fast dv/dt transition at QR pin during mainMOSFET turn on;

FIG. 6A illustrates example waveforms for the system of FIGS. 4 and 5when the AC Line voltage is low (e.g., 50 Vrms); and

FIG. 6B is a zoomed view of a portion of FIG. 6A.

DETAILED DESCRIPTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention that may be embodied in variousand alternative forms. The figures are not necessarily to scale; somefeatures may be exaggerated or minimized to show details of particularcomponents. Therefore, specific structural and functional detailsdisclosed herein are not to be interpreted as limiting, but merely as arepresentative basis for teaching one skilled in the art to variouslyemploy the present invention.

Amplifiers, including Class D amplifiers, may use flyback converters toprovide bias power to various circuits and ICs on the primary andsecondary side of the system. These flyback power supplies typically useof the shelf controller ICs. To improve efficiency, quasi-resonant andactive clamp topology flyback converters are used as the bias supply.Their controller IC's require that the voltage on their quasi-resonantpin go high prior to complementary MOSFET turn on. However, at low ACline and during system turn off, the voltage at the ICs resonant pin maytake a longer period of time to transition to a high level and canresult in the main MOSFET turning on again after the IC's internal timeout. This may cause hard switching, ringing on the switch node, andsemiconductor failure, leading to shutdown due the lack of bias power.Existing systems using universal AC inputs (85 Vrms-264 Vrms) ensureturn on and off at relatively higher AC voltages (e.g. >70 Vrms) toprevent system operation at lower AC input voltages.

Currently, AC/DC rectifiers with power factor correction (PFC) mayinclude a boost converter for PFC. This converter regulates the DC bustypically at 400V and is used to provide DC voltage to the flybackconverter input after system turn on instead of providing a rectifiedvoltage directly from the AC mains. However, the issues still exist atturn on, as well as at turn off at low voltage levels.

Disclosed herein is a system that ensures appropriate pulse widthmodulation (PWM) pulses are obtained at low line and when the amplifiersystem is off by including a transition component. In one example, thetransition component may be a DC offset included on the quasi-resonate(QR) pin of the controller IC in order to increase the amplitude of thevoltage thereon. In another example, a resistor may be arranged betweenthe QR pin and the output pin of the controller IC. The resistor adds DCoffset and facilitates a fast voltage change transition at the QR pinduring main MOSFET turn on.

These embodiments help prevent hard switching and potentialsemiconductor failure. Further, higher voltage rated components, such ascapacitors and semiconductors, are not required, reducing system costs.With the addition of the DC Offset and/or resistor, the system may startup at lower AC line voltage resulting in a lower inrush current.Further, lower stresses on system components such as semiconductors, atlow AC line, increases efficiencies of the system in a cost-effectivemanner.

FIG. 1 illustrates an example system diagram for an amplifier system 100having a primary side 104 and a secondary side 106. A flyback converter102 is arranged on the primary side 104 of the system 100. FIG. 2illustrates the zoomed in primary side 104 of the system 100 of FIG. 1 .Referring to both figures, the flyback converter 102 may include a pairof metal oxide silicon field effect transistors (MOSFETs) 110, 112configured to require a high voltage at the flyback converter 102 priorto turning on. As is the case in a typical flyback system, the switchingoccurs at the primary side 104. The switch node 122 is arranged betweenthe two MOSFETs 110, 112 as shown in FIG. 2 .

The system 100 includes a controller IC 120. The IC 120 is illustratedas an eight-pin IC, but may include any number of pins (e.g., 16 pins,etc.). In this example, the IC 120 may include a quasi-resonant (QR)pin. The IC 120 includes a supply voltage V_(CC) pin configured to turnon so long as the voltage at the pin is above a voltage threshold. TheIC is disabled if the voltage at the Vcc pin falls below the threshold.

Other pins may include a soft start (SS) pin that charges and ramps upwith an internal current generator. As the current ramps up, the currentat a current sense (CS) pin increases linearly, affecting the dutycycle. The SS pin is discharged when the supply voltage at the V_(CC)falls below the threshold. A COMP pin may activate a burst-modeoperation if the pin recognizes a voltage below an internal threshold.The OUT pin of the IC 120 may transmit the PWM drive to a driver IC 130.

FIG. 3A illustrates example waveforms for the system of FIGS. 1 and 2when the AC line voltage is low (e.g., 50 Vrms). The first waveform 302illustrates the gate-source voltage V_(gs) of the MOSFET 112. The secondwaveform 304 illustrates the drain-source voltage V_(ds) of the MOSFET112. The third waveform 306 illustrates a QR voltage at the QR pin ofthe controller IC 120.

As illustrated, the drain-source voltage V_(ds) peaks when thegate-source voltage V_(gs) drops, with at least one intermittent peakwhile the gate-source voltage is low. The voltage at the QR pin of thecontroller IC 120 mimics the drain-source voltage V_(ds) and peaks whenthe gate-source voltage V_(gs) drops.

FIG. 3B is a zoomed view of portion 314 of FIG. 3A. The first waveform302 illustrates the gate-source voltage V_(gs) over time. As explainedabove, the complementary MOSFET 110, will turn on once the voltage atthe QR pin of the controller IC 120 exceeds the threshold voltage. Asshown in FIG. 3B, voltage is slow to exceed this threshold. This resultsin a bad V_(gs) pulse as shown at 316 in FIG. 3B. This is due, at leastin part, to the slow voltage change at the QR pin at low AC line,causing hard switching to occur for MOSFET 112 in FIG. 2 .

The second waveform 304 illustrates the voltage over time at thecontroller QR pin at low AC line (e.g., less than 70 Vrms AC input). Asillustrated, the change in voltage (dv/dt) is slow after the main MOSFET112 turns OFF. The third waveform 306 illustrates the slow dv/dt changein voltage over time at the switch node 122 which is the same as thedrain to source voltage (V_(ds)) of main MOSFET 112. This slowtransition at the controller IC 120 QR pin, results in the main MOSFET112 turning ON again as shown by the incorrect short V_(gs) pulse 316 inFIG. 3B. Also, notice that this incorrect pulse results in hardswitching at the switch node 122 as shown by the abrupt drop in mainMOSFET 112 V_(ds) voltage (switch node voltage) as shown at 320 in FIG.3B. when the voltage meets the threshold.

Thus, the voltage at the ICs resonant pin for the systems in FIGS. 1 and2 may take a longer period of time to transition to a high level and canresult in the main MOSFET turning on again after the IC's internal timeout. This may cause hard switching, ringing on the switch node, andsemiconductor failure, leading to system shutdown due the lack of biaspower. Existing systems may use universal AC inputs (85 Vrms-264 Vrms)to ensure turn on and off at relatively higher AC voltages (e.g. >70Vrms) and to prevent system turn on at lower AC input voltages.

FIG. 4 illustrates a zoomed in example system diagram for an amplifiersystem 400 having a flyback converter 102 arranged on the primary side104 of the system 400. As explained above with respect to FIGS. 1 and 2, the flyback converter 102 includes a pair of field-effect transistor(MOSFETs) 110, 112 configured to require a high voltage at the flybackconverter 102 prior to turning on. As is the case in a typical flybacksystem, the switching occurs at the primary side 104. The switch node122, is arranged between the two MOSFETs 110, 112.

The system 400 includes a controller IC 120. In this example, the IC 120may include the quasi-resonant (QR) pin and the supply voltage VCC pinconfigured to turn on so long as the voltage at the pin is above thethreshold. The IC is disabled if the voltage at the VCC pin falls belowthe threshold. Other pins may include the soft start (SS) pin, thecurrent sense (CS) pin, and the COMP pin, among others.

The system 400 may include a DC offset 406 arranged at the QR pin of theIC 120. The DC offset 406 may have a fast voltage change transitioncircuit. The DC offset, which is the amplitude displacement from zero,may allow for the correct PWM pulses to be obtained at the low AC lineand during system turn off. This aids in preventing hard switching andpotential semiconductor failure. By increasing the amplitude of thevoltage at the QR pin, the transition between on and off may be slow,consistent, and less abrupt. Further, the IC 120 will not time out.

FIG. 5 illustrates a zoomed in example system diagram similar to FIG. 4for an amplifier system 500 having the flyback converter 102 arranged onthe primary side 104 of the system 500. As explained above with respectto FIG. 4 , the flyback converter 102 includes a pair of metal oxidesilicon field effect transistors (MOSFETs) 110, 112.

The system 500 includes a resistor 506 arranged between the IC's QR pinand the output pin. The resistor 506 may facilitate a DC offset and fastvoltage change transition at the QR pin that prevents the incorrectrogue PWM turn on pulse for MOSFET 112. This prevents hard switching ofthe main MOSFET pulse.

FIG. 6A illustrates example waveforms for the system of FIGS. 4 and 5when the AC line voltage is low (e.g., 50 Vrms) and after the use of atransition component such as the DC offset 406 and/or the resistor 506of FIGS. 4 and 5 respectively. The first waveform 602 illustrates thedrain-source voltage V_(ds) of the main MOSFET 112. The second waveform604 illustrates the gate-source voltage V_(gs) of the main MOSFET 112.The third waveform 606 illustrates a QR voltage at the QR pin of thecontroller IC 120. The fourth waveform 608 illustrates the gate-sourcevoltage V_(gs) of the complementary MOSFET 110.

Similar to FIG. 3A, the drain-source voltage of MOSFET 112 starts goinghigh after its gate-source voltage goes low. The voltage at the QR pinof the controller IC 120 mimics the drain-source voltage and startsgoing high when the gate-source voltage drops.

FIG. 6B is a zoomed view of portion 614 of FIG. 6A. Unlike the voltageat the QR pin shown in FIG. 3 , the voltage is now greater than thecontroller IC QR pin threshold due to the added DC offset. There is nohard switching like the example in FIG. 3B, nor are there anyinadvertent V_(gs) pulses.

Thus, the voltage at the IC QR resonant pin for the systems in FIGS. 4and 5 does not false trigger due to the added transition component(e.g., the DC offset 406 and/or the resistor 506). The V_(gs) pulses areclean and alternating, allowing for smooth switching at the switch node.

The DC offset at the flyback controller's resonant pin allows thecorrect PWM pulses to be obtained at low AC line as well as duringsystem turn off. The DC offset and resistor between the QR pin andoutput pin prevent hard switching and potential failure ofsemiconductors that can lead to shutdown due to a lack of bias power.Capacitors and semiconductors with higher voltage ratings are notrequired and allows for cost savings. Furthermore, components withhigher voltage ratings have slower switching speeds which may contributeto additional system losses. The system described herein allows forstartup at lower AC line voltages, resulting in lower inrush currents.The system also allows for a reduction of switching losses and reductionin electrical stress (e.g., overvoltage, switching losses, etc.) on thesemiconductors at low AC line. This further adds to increasing thesystem's efficiencies.

The descriptions of the various embodiments have been presented forpurposes of illustration, but are not intended to be exhaustive orlimited to the embodiments disclosed. Many modifications and variationswill be apparent to those of ordinary skill in the art without departingfrom the scope and spirit of the described embodiments.

Aspects of the present embodiments may be embodied as a system, methodor computer program product. Accordingly, aspects of the presentdisclosure may take the form of an entirely hardware embodiment, anentirely software embodiment (including firmware, resident software,micro-code, etc.) or an embodiment combining software and hardwareaspects that may all generally be referred to herein as a “module” or“system.” Furthermore, aspects of the present disclosure may take theform of a computer program product embodied in one or more computerreadable medium(s) having computer readable program code embodiedthereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readable signalmedium or a computer readable storage medium. A computer readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, or device, or any suitable combination of the foregoing. Morespecific examples (a non-exhaustive list) of the computer readablestorage medium include the following: an electrical connection havingone or more wires, a portable computer diskette, a hard disk, a randomaccess memory (RAM), a read-only memory (ROM), an erasable programmableread-only memory (EPROM or Flash memory), an optical fiber, a portablecompact disc read-only memory (CD-ROM), an optical storage device, amagnetic storage device, or any suitable combination of the foregoing.In the context of this document, a computer readable storage medium maybe any tangible medium that can contain, or store a program for use byor in connection with an instruction execution system, apparatus, ordevice.

Aspects of the present disclosure are described above with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodiments of thedisclosure. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general-purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, enable the implementation of the functions/acts specified inthe flowchart and/or block diagram block or blocks. Such processors maybe, without limitation, general purpose processors, special-purposeprocessors, application-specific processors, or field-programmable.

The flowcharts and block diagrams in the figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods and computer program products according to variousembodiments of the present disclosure. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It should also be notedthat, in some alternative implementations, the functions noted in theblock may occur out of the order noted in the figures. For example, twoblocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each block of the block diagrams and/or flowchart illustration, andcombinations of blocks in the block diagrams and/or flowchartillustration, can be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions.

While exemplary embodiments are described above, it is not intended thatthese embodiments describe all possible forms of the invention. Rather,the words used in the specification are words of description rather thanlimitation, and it is understood that various changes may be madewithout departing from the spirit and scope of the invention.Additionally, the features of various implementing embodiments may becombined to form further embodiments of the invention.

What is claimed is:
 1. An amplifier system, comprising: at least oneinput source; a flyback converter including a pair of complementarymetal oxide silicon field effect transistor (MOSFETs); a controllerintegrated circuit (IC) having a quasi-resonant (QR) pin and configuredto provide a biased drive current to the flyback converter, and atransition component arranged at the controller IC and configured tocorrect pulse width modulation at the IC to ensure the voltage at atransition pin of the IC is above a predefined threshold during aresonant transition.
 2. The system of claim 1, wherein the transitioncomponent is a DC offset arranged in series with the QR pin of thecontroller IC to offset the voltage above the predefined threshold. 3.The system of claim 1, wherein the transition component includes aresistor arranged between the QR pin and an output pin of the controllerIC.
 4. The system of claim 1, wherein the transition component is a fastvoltage change transition circuit configured to correct PWM pulses to beobtained at a low current line.
 5. The system of claim 1, wherein thetransition component is a fast voltage change transition circuitconfigured to correct PWM pulses to be obtained when the system is off.6. The system of claim 1, wherein the transition component increases thevoltage amplitude at the QR pin to prevent hard switching.
 7. An audioamplifier system employing flyback converters to provide a bias supply,comprising: at least one input source; a flyback converter including apair of complementary metal oxide silicon field effect transistor(MOSFETs); a controller integrated circuit (IC) having a quasi-resonant(QR) pin and configured to provide a biased drive current to the flybackconverter, and a transition component arranged at the controller IC andconfigured to correct pulse width modulation at the IC to ensure thevoltage at a transition pin of the IC is above a predefined thresholdduring a resonant transition.
 8. The system of claim 7, wherein thetransition component is a DC offset arranged in series with the QR pinof the controller IC to offset the voltage above the predefinedthreshold.
 9. The system of claim 7, wherein the transition componentincludes a resistor arranged between the QR pin and an output pin of thecontroller IC.
 10. The system of claim 7, wherein the transitioncomponent is a fast voltage change transition circuit configured tocorrect PWM pulses to be obtained at a low current line.
 11. The systemof claim 7, wherein the transition component is a fast voltage changetransition circuit configured to correct PWM pulses to be obtained whenthe system is off.
 12. The system of claim 7, wherein the transitioncomponent increases the voltage amplitude at the QR pin to prevent hardswitching.
 13. An amplifier system, comprising: at least one inputsource; a flyback converter including a pair of complementary fieldeffect transistors (FETs); a controller integrated circuit (IC) having aquasi-resonant (QR) pin and configured to provide a biased drive currentto the flyback converter, and a transition component arranged at thecontroller IC and configured to correct pulse width modulation at the ICto ensure the voltage at a transition pin of the IC is above apredefined threshold during a resonant transition, wherein thetransition component is a DC offset arranged in series with the QR pinof the controller IC to offset the voltage above the predefinedthreshold.
 14. The system of claim 13, wherein the transition componentis a fast voltage change transition circuit configured to correct PWMpulses to be obtained at a low current line.
 15. The system of claim 13,wherein the transition component is a fast voltage change transitioncircuit configured to correct PWM pulses to be obtained when the systemis off.
 16. The system of claim 13, wherein the transition componentincreases the voltage amplitude at the QR pin to prevent hard switching.